It is known to drop balls made of foamable polyurethane material into the cavities inside car pillars so that these form a barrier. However, the material does not adhere to the steel nor do they necessarily and reproducibly block the cavity to be filled.
It is also known to use the technique of direct injection of a two-component polyurethane system with volatile fluoro-chlorohydrocarbons (freon) but this involve a separate operation in the production process.
It is also known from JP 55046940 to expand a sheet or tube of a thermoplastic resin and a foaming agent such as azodicarbonamide in situ between an inner and outer pipe to provide heat insulation. JP 60090737 also discloses an innerliner obtained by inserting a resin cylinder capable of being foamed by heating and externally heating a tubular construction to expand the tubular resin. The inner pipe is withdrawn. The tubular resin may contain a variety of possible olefinic copolymers but copolymers of ethylene methyl acrylate are not disclosed. The material to be foamed is present in cylinder with a high surface to volume ratio. Heat is transmitted to the material from an external heat source through heat-conductive metal. The foaming period is likely to be short, the foaming controllable and commencing from the outside or surface of the material.
L+L Products Inc of Michigan USA supply adhesive sealants of heat activatable, curable and expandable materials for moisture and sound insulation in automative applications. No detailed information is available as to the polymer and the manner of application but sealants may be in extruded form.
U.S. Pat. No. 4,480,054 discloses a foamable curable composition of a carboxylic acid co- or terpolymer with a terpolymer containing possibly methylacrylate as a termonomer. Such materials may have a low softening points so that foams are unstable if exposed to elevated temperatures for a prolonged period. The carboxylic acide groups may retard curing, aggravating form instability at high temperatures.
U.S. Pat. No. 4499210 discloses a foamable composition of amongst others ethylene alkylacrylate polymers but the foam is open cell and does hence not possess suitable barrier properties.
GB-1227454 discloses foamable mixtures of copolymers of ethylene with esters of ethylenically unsaturated acids but using physical blowing agents such as propane etc. Expansion characteristics cannot be finely controlled.
GB-1211451 and GB-1447825 disclose foamable mixtures of ethylene copolymers in which pressure is used to control action of an expanding agent which would not permit in situ controlled expansion. GB-1044757 discloses a foamable, curable composition including (Example 2 a copolymer of ethylene and ethylacrylate) using special peroxides to permit completion of crosslinking or curing until after foaming has taken place in a closed mould at 170.degree. C. The part is moulded and emerges from the mould in a foamed condition. In situ expansion under a wide possible range of curing temperatures would be difficult.
It is the object of the invention to provide a foamable shaped part which can be mounted early in a car assembly operation, free of surrounding metal walls, permits those walls to be treated and then expands in situ to contact the walls and adhere thereto to form a closed-cell foam plug.
It is another object to provide a composition for shaping into a foamable part which has characteristics suitable for processing as shown above i.e. which
(1) permits polymer and foaming/curing package to be blended and shaped without foaming or curing;
(2) which expands, using surrounding air and internally supplied heat from a relatively low surface area to volume ratio;
(3) which delays curing until after appreciable expansion has taken place so as to provide good adhesion at the surface;
(4) which then cures and remains in position without foam collapse during exposure at elevated temperatures without risk of metal corrosion.